1. Field of the Invention
The present invention relates to a wireless communication device and mobile station, and in particular to a system using wireless communication devices and mobile stations is the W-CDMA (UMTS) mobile communication system.
2. Description of the Related Art
Standardization is currently progressing within the 3GPP (3rd Generation Partnership Project) on the W-CDMA (UMTS) scheme, one scheme for a third generation mobile communication systems. HSDPA (High Speed Downlink Packet Access), which provides a maximum transmission speed of approximately 14 Mbps, has been specified as one theme of the standardization.
HSDPA is characterized in that it employs an adaptive coding modulation scheme, for example, switching adaptively between a QPSK modulation scheme and a 16-QAM scheme depending on the wireless environment between the base station and mobile station.
HSDPA furthermore employs an H-ARQ (Hybrid Automatic Repeat reQuest) scheme. Under H-ARQ, when a mobile station detects an error in the data received from the base station, a retransmission request is made from the mobile station to the base station, and the data is retransmitted from the base station. The mobile station then performs error correction decoding using both the already received data and the retransmitted received data. Thus, H-ARQ increases the benefits of error correction decoding and reduces the number of retransmissions by effectively using already received data.
The main wireless channels used in HSDPA include HS-SCCH (High Speed-Shared Control Channel), HS-PDSCH (High Speed-Physical Downlink Shared Channel) and HS-DPCCH (High Speed-Dedicated Physical Control Channel).
HS-SCCH and HS-PDSCH are both downlink (i.e., in the direction from the base station to the mobile station) common channels; HS-SCCH is a control channel for transmitting various parameters relating to the data transmitted on HS-PDSCH. The various parameters include, for instance, modulation type information indicating what modulation scheme is to be used for transmitting data on HS-PDSCH, spreading code assignment numbers (code numbers), information on the pattern of rate matching performed on the transmitted data, and the like.
HS-DPCCH, on the other hand, is a dedicated uplink control channel, in the direction from the mobile station to the base station; it is used by a mobile station to transmit ACK and NACK signals, depending on whether the data received via HS-PDSCH was received properly or not. If the mobile station failed to receive data (when the received data has a CRC error or the like), a NACK signal would be transmitted from the mobile station to the base station, whereupon the base station would execute retransmission control.
The HS-DPCCH is also used by the mobile station to periodically transmit to the base station the results of determination of the reception quality (e.g., SIR) of the signal received from the base station as a CQI (Channel Quality Indicator). The base station evaluates the goodness of the downlink wireless environment based on the received CQIs, and switches for instance to a modulation scheme that allows data to be transmitted at higher speeds if the environment is good. If the wireless environment is not good, the base station adaptively switches to a modulation scheme whereby data is transmitted at lower speed, etc.
Channel Structure
Next, the channel arrangement involved in HSDPA will be explained.
FIG. 1 is a diagram illustrating the channel arrangement involved in HSDPA. Since W-CDMA employs a code division multiplexing scheme, each channel is separated by means of a code.
First, the channels which have not been explained will be briefly described.
CPICH (Common Pilot Channel) and P-CCPCH (Primary Common Control Physical Channel) are respectively downlink common channels.
CPICH is a channel used by the mobile station as a timing reference for channel estimation, cell search and other downlink physical channels within the same cell; it is a channel used to transmit the so-called pilot signal. P-CCPCH is a channel for transmitting broadcast information.
Next, the timing relationship of the various channels will be described.
As shown in FIG. 1, each channel comprises one frame (10 ms) of 15 slots. As explained earlier, CPICH is used as a reference for other channels, so the head of the frame of P-CCPCH and HS-SCCH is aligned with the head of the CPICH frame. Here, the head of the HS-PDSCH frame is delayed by two slots relative to HS-SCCH and the like. This is in order to provide advance notice, via the HS-SCCH, of the demodulation type information and spreading code information which the mobile station needs in order to perform demodulation of the HS-PDSCH. Therefore, the mobile station selects the appropriate demodulation scheme and despreading code according to the information provided in advance on HS-SCCH to execute the processing of HS-PDSCH demodulation, etc.
Furthermore, HS-SCCH and HS-PDSCH comprise subframes of three slots.
The above was a simple description of the HSDPA channel arrangement.
Next, the content and coding procedure of the data transmitted on HS-SCCH will be described.
Data Transmitted on HS-SCCH
The following data are transmitted on HS-SCCH. Each datum is used for reception processing of HS-PDSCH, on which transmission takes place with a two slot delay.
(1) Xccs (Channelization Code Set information)
(2) Xms (Modulation Scheme information)
(3) Xtbs (Transport Block Size information)
(4) Xhap (Hybrid ARQ Process information)
(5) Xrv (Redundancy and constellation Version)
(6) Xnd (New Data indicator)
(7) Xue (User Equipment identity)
(1) through (7) will be described.
(1), Xccs, is a datum indicating the spreading code used for transmitting data on HS-PDSCH (e.g., a datum indicating a combination of multicode number and code offset), and consists of 7 bits.
(2), Xms, is a datum indicating whether the modulation scheme used on HS-PDSCH is QPSK or 16-QAM, and consists of 1 bit.
(3), Xtbs, is a datum used for computing the transport block size of the data transmitted on HS-PDSCH (the size of the data transmitted in one subframe of HS-PDSCH), and consists of 6 bits.
(4), Xhap, is a datum indicating the H-ARQ process number, and consists of 3 bits. A base station basically cannot determine whether or not a mobile station was able to receive data until the base station receives an ACK or NACK. However, if it were to wait until the ACK or NACK was received before transmitting a new data block, the transmission efficiency would decrease. Thus, in order to enable transmission of new data blocks before receiving an ACK or NACK, a process number is defined for each data block transmitted in subframes, and the mobile station is made to perform reception processing in pieces based on the process number. Namely, under the condition that the base station will assign the same process number when performing retransmission as the process number assigned to the previously sent transport block, each transport block is given the corresponding process number, which is transmitted in advance via HS-SCCH as the Xhap.
Therefore, the mobile station classifies data received via the HS-PDSCH based on the received Xhap, and performs discrimination of new transmission or retransmission based on Xnd, which will be described below, in the stream of data for which the same process number was indicated via HS-SCCH, as well as combining new data and resent data, etc. (H-ARQ processing, etc.).
(5), Xrv, is a datum which indicates the redundancy version (RV) parameter (s, r) and constellation version parameter (b) for HS-PDSCH retransmission, and consists of 3 bits.
For Xrv, there is a first technique (Incremental Redundancy) whereby the parameters are updated for new transmission and retransmission, and a second technique (Chase Combining) whereby the parameters are not changed for new transmission or retransmission.
In the first technique, the puncture pattern and the like varies, so the bits to be transmitted change between new transmission and retransmission, while in the second technique, they do not change.
(6), Xnd, is a datum indicating whether a block transmitted on HS-PDSCH is a new block or a resent block, and consists of one bit. For example, when transmitting a new block, it would be switched from 0 to 1 or from 1 to 0, while when retransmitting, the same value would be used as before, without switching.
For example, when performing a sequence of new transmission, retransmission, new transmission, retransmission, retransmission; new transmission, the Xnd would change in the order 1, 1, 0, 0, 0, 1.
(7), Xue, is a datum indicating the identification information of the mobile station, and consists of 16 bits.
FIG. 2 is the structure of the HS-SCCH coding unit.
In FIG. 2, 1 is a coding unit, 2 is a rate matching unit, 3 is a multiplication unit, 4 is a CRC computation unit, 5 is a multiplication unit, 6 is a coding unit, 7 is a rate matching unit, 8 is a coding unit, and 9 is a rate matching unit.
The operation of each block will be described next.
(1) Xccs (x1,1-x1,7), represented in 7 bits, and (2) Xms (x1,8), represented in 1 bit, are inputted into the coding unit 1 as a datum with a total of 8 bits. Here, the first half of the subscript signifies that this relates to data transmitted in the first slot, while the number of the second half, separated by a comma (,), signifies the number of the bit.
Now, the coding unit 1 appends 8 tail bits to the inputted data, and performs convolutional coding at a code rate of 1/3 on a total of 16 bits. Thus, the encoded data becomes a total of 48 bits, and is given to the rate matching unit 2 as z1,1-z1,48. The rate matching unit 2 performs puncturing, repetition, etc. of specific bits, and outputs the bits adjusted to the number of bits (assumed to 40 here) that will fit into the first slot (r1, 1-r1,40).
Data from the rate matching unit 2 are multiplied by c1-c40 in the multiplication unit 3 and outputted as s1,1-s1,40, and are transmitted in the first slot (first part) of HS-SCCH in FIG. 1, which is the slot at the head of a subframe.
Here, c1-c40 are obtained by adding 8 tail bits to the data from (7) Xue (Xue1-Xue16) and then convolutionally encoding, in coding unit 8, it at a coding rate of 1/2 to obtain b1-b48, which are further subjected, in rate matching unit 9, to the same bit adjustment as in the rate matching unit 2.
Furthermore, the 6-bit (3) Xtbs (x2,1-x2,6), 3-bit (4) Xhap (x2,7-x2,9), 3-bit (5) Xrv (x2,10-x2,12) and 1-bit (6) Xnd (x2, 13), are inputted as a total of 13 bits y2,1-y2,13, with the 16 bits y2,14-y2,29 further added for a total of 29 bits, y2,1-y2,29, into the coding unit 6.
Here, y2,14-y2,29 are obtained by performing CRC computation on the total of 21 bits of (1) through (6) in the CRC computation unit 4, and multiplying the results of that computation, c1-c16, by (7) Xue (xue1-xue16).
The y2,1-y2,29 inputted into the coding unit 6 have 8 tail bits added thereto and are convolutionally encoded at a coding rate of 1/3 and inputted as 111 bits, x2,1-z2,111, into the rate matching unit 7.
The rate matching unit 7 outputs 80 bits, r2,1-r2,80 by means of processing such as the aforementioned puncturing, and these r2,1-r2,80 are transmitted in the second and third slot (second part) of the one subframe on HS-SCCH in FIG. 1.
As described above, the data of (1) and (2) are transmitted in a first part, while (3) through (6) are transmitted in a second part, thus being transmitted in distinctly in separate slots, but these data are subjected to a common CRC computation, with the CRC computation result being transmitted in the second part, so detection of reception error becomes possible once both the first and second part are completely received.
Furthermore, since the data transmitted in the first slot is multiplied by (7) Xue in the multiplication unit 3 after undergoing convolutional coding by the coding unit 1, when data addressed to another station is received in the first slot, the likelihood generated in the decoding process will be smaller compared to if it were addressed to this station, so a comparison of the likelihood to a reference value can reveal that the possibility of it not being addressed to this station is high.
Coding of Data Transmitted on HS-PDSCH
Next, the process leading to transmission of data via HS-PDSCH will be described using a block diagram.
FIG. 3 is a diagram which illustrates a transmission device according to the present invention.
The transmission device (wireless base station) of a W-CDMA communication system compatible with the above-described HSDPA will be described as an example transmission device. This can also be applied to transmission devices in other communication systems.
In the drawing, 10 represents a control unit which sequentially outputs the transport data (the data transmitted within one subframe) to be transmitted via HS-PDSCH, as well as controlling the various units (11 through 26, etc.). The values of (1) through (7) described in FIG. 2 are assigned by this control unit 10.
Since HS-PDSCH is a shared channel, it is allowed for successively outputted data to be addressed to different mobile stations.
11 represents a CRC attachment unit which performs a CRC computation on the successively inputted transport data (data transmitted within the same wireless frame) and attaches the CRC computation result to the tail of this transport data, and 12 represents bit scrambling unit which scrambles the transport data with the CRC computation result attached thereto in bit units to impart randomness to the transmitted data.
13 represents a code-block segmentation unit which segments (e.g., into two equal parts) the inputted bit-scrambled transport data when it exceeds a certain data length, in order to prevent increase in computational volume of the receiving side decoder due to excessive length of the data to be encoded in the following channel coding, and the like. The drawing illustrates output in a case where the inputted data length exceeded a certain data length and was divided into two equal parts (segmented into a first data block and second data block). Of course, cases where the number of segments is other than two are also possible, as are cases where the data is divided not into equal parts but into different data lengths.
14 represents a channel coding (encoding) unit which performs error correction coding separately on each segmented datum. Here, it is assumed that a turbo coder is used for the channel coding unit 14.
Therefore, the first output of the channel coding unit, for the first block, contains: the important systematic bits (U), which are the same data as the data to be coded; the first redundancy bits (U′) obtained by convolutionally coding the systematic bits (U); and the second redundancy bits (U″) obtained by interleaving the systematic bits and then convolutionally coding in the same manner. Likewise, the second output contains the systematic bits (U), first redundancy bits (U′) and second redundancy bits (U″) for the second block.
15 represents a bit separation unit which separates the first block and second block, serially inputted from the channel coding unit 14 (turbo coder), into the systemic bits (U), first redundancy bits (U′) and second redundancy bits (U″), and outputs them.
16 represents a first rate matching unit which performs rate matching, e.g. puncturing, on the input data (the data of all separated blocks when separated into multiple blocks) in order to make it fit into a specific region of the following virtual buffer unit 17.
17 represents a virtual buffer unit, in which a region is set by the control unit 10 in accordance with the reception processing capacity of the mobile station to be transmitted to, and which stores data rate-matched by the first rate matching unit 16 in that region. During retransmission, the processing from the CRC attachment unit to the first rate matching unit can be omitted by outputting the stored data, but when one wishes to change the coding rate during retransmission, etc., it is preferable not to use the stored data but rather to re-output the transmission data held by the control unit. It is also possible to not provide an actual buffer for the virtual buffer unit 17 and to have the data pass through directly. In this case, resent data would be re-outputted from the control unit 10.
18 represents a second rate matching unit for adjusting the data length with control unit 10 to one that can fit inside the designated subframe; it adjusts the data length of the inputted data to the designated data length by performing puncturing and repetition on it.
This second rate matching unit 18 performs rate matching according to the previously described RV parameter.
Namely, according to the RV parameter, when s=1, rate matching is carried out so as to leave as many systematic bits as possible; on the other hand, when s=0, it is permitted for the systematic bits to be reduced and for more redundancy bits to remain. Furthermore, rate matching and puncturing are performed based on a pattern according to r.
19 represents a bit collection unit which arranged the data from the second rate matching unit 19 into a plurality of bit sequences. Namely, the data of the first block and the data of the second block are arranged according to a specific bit arrangement method to output a plurality of bit sequences serving to indicate the signal points on a phase plane. Since the 16-QAM modulation scheme is used in this example, the bit sequence consists of four bits; when using a 64-QAM modulation scheme, the bit sequence would be made six bits, and when using a QPSK modulation scheme, the bit sequence would be made two bits.
20 segments and outputs bit sequences into the same number of systems as the number of the spreading code (code number) provided by the control unit 10. Namely, it represents a physical channel segmentation unit which, when the code number in the transmission parameters provided by the control unit 10 is N, maps the inputted bits sequentially to 1 through N systems and outputs them.
21 is an interleaving unit which performs interleaving on the bit sequences of N systems and outputs them.
22 is a constellation rearrangement unit for 16-QAM, which is able to rearrange bits within, each inputted bit sequence. Bit rearrangement is carried out according to the earlier described constellation version. Examples of bit rearrangement include substituting high order and low order bits; it is preferable for bit substitution to be carried out by the same rule for multiple bit sequences.
23 is a physical channel mapping unit which maps the bit sequences of N systems to the corresponding spreading section of the following spreading unit 24.
24 is a spreading unit which comprises a plurality of spreading sections, each of which outputs the corresponding I and Q voltage based on each bit sequence of N systems, performing spreading with a different spreading code in each case and outputting the result.
25 represents a modulating unit which combines the signals spread by the spreading unit 24, and based thereon, performs amplitude phase modulation, for instance by the 16-QAM modulation scheme, amplifies by means of a variable gain amplifier, performs frequency conversion to a wireless signal, and then outputs the wireless signal to the antenna to enable transmission.
Since. HSDPA allows multiplexing of signals addressed to other mobile stations by means of spreading codes in subframes of the same timing, it is preferably to provide multiple sets of 10 through 25 and of the variable gain amplifier, etc. (which will be referred to as transmission sets), and to combine the output signals of the variable gain amplifiers, then frequency-convert them in common, and then transmit the result to the antenna. Of course, since separation by code is necessary, the spreading code used by the spreading unit 24 of each transmission set would differ so as to allow separation.
26 represents a reception unit, which receives signals from a mobile station received via HS-DPCCH or the like, and provides the ACK or NACK signal, CQI, etc. to the control unit 10.
As described above, when an ACK signal is received, the next new data is transmitted, while in the case of a NACK signal or if there is no response within a specific period of time, the control unit 10 performs retransmission control to retransmit the transmitted data. Retransmission is limited to a set maximum number of retransmissions; if the maximum number of retransmission is reached without receiving an ACK signal from the mobile station, the control unit 10 provides control to switch to transmission of the next new data.
In cases where no maximum number of retransmission is defined, it is also possible to start a timer from a new transmission, and switch to transmission of the next new data if a specific time is detected to have elapsed with no ACK signal having been received.
The foregoing was a description of the designations and operation of each unit.
Matters relating to the above-described HSDPA are disclosed for instance in 3rd Generation Partnership Project: Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (3G TS 25.212) and 3rd Generation Partnership Project: Technical Specification Group Radio Access Network; Physical layer procedures (FDD) (3G TS 25.214).
According to the background art described above, by means of the data (Xnd) for discriminating between new transmission and retransmission, a wireless communication device is able to determine whether received data (HS-PDSCH) is a new transmission or retransmission, but errors may occur in this data (Xnd), and being unable to detect a change in Xnd, the next change in Xnd may be erroneously taken to indicate a retransmission.
In particular in the case of a wireless communication device which combines already received data with retransmitted data, if it cannot correctly discriminate between new transmission and retransmission, it will end up making an incorrect combination, leading to a reception error.
Therefore, a need arises to reduce the occurrence of reception errors.